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Full text of "Chromosomes and phylogeny in Crepis. II. The relationships of one hundred eight species"

CHROMOSOMES AND PHYLOGENY 
IN CREPIS 

II. THE RELATIONSHIPS OF 
ONE HUNDRED EIGHT SPECIES 

BY 
ERNEST B. BABCOCK and DONALD R. CAMERON 



University of California Publications in Agricultural Sciences 

Volume 6, No. 11, pp. 287-324, 18 figures in text 

Issued October 11, 1934 

Price, 50 cents 



University of California Press 
Berkeley, California 



Cambridge University Press 
London, England 



PRINTED IN THE UNITED STATES OF AMERICA 






CHROMOSOMES AND PHYLOGENY IN CREPIS 

II. THE RELATIONSHIPS OF 
ONE HUNDRED EIGHT SPECIES 

BY 

ERNEST B. BABCOCK and DONALD R. CAMERON 



INTRODUCTION 

The first paper of this series (Hollingshead and Babcock, 1930), pre- 
sented data on the number and morphology of the chromosomes in 
sixty-seven species of Crepis and three other species belonging in closely 
related genera. Since then it has been possible to study the chromosomes 
of fifty additional species and subspecies, and it is now possible to discuss 
the bearing of all these chromosome studies on the phylogenetic relation- 
ships of about half the species in the genus. 

Our conception of the fundamental principles of biological classifica- 
tion remains essentially as set forth in the contribution cited. More 
recently one of us (Babcock, 1931) has discussed the species-concept 
and emphasized the value of chromosome number and morphology as 
one criterion of classification according to natural relationship. In 
Crepis this criterion has proved especially valuable. The genus is large 
and much diversified, many species are rare or little known, and from 
comparative morphology of the plants alone it is often difficult to draw 
definite conclusions. From a comparative study of the chromosomes it 
is sometimes possible to obtain the first clue concerning the manner of 
origin of certain species, and such clues have led to the discovery of 
confirmatory evidence from other criteria. 

CYTOLOGICAL MATERIAL AND METHODS 

Chromosomes are notoriously variable in appearance, even within a 
single individual, according to the conditions under which they are 
studied. Due precautions have therefore been observed for the study of 
comparable material. As in our earlier work and in most of the other 
researches in this field, the appearance of the chromosomes at mitotic 
metaphase has been used. Considerable refinement in the technique of 
comparing size and shape of the chromosomes has been attained by 
making camera lucida drawings of the best available diploid groups, 
identifying the several pairs present in the group, and deriving there- 
from the members of the haploid genom. The illustrations in the present 
paper depict these haploid genoms all drawn to the same scale. 

[287] 



288 



University of California Publications in Agricultural Sciences [Vol. 6 



TABLE 1 

Chromosome Numbers in Fifty-five Species, Subspecies, and Forms not 
Previously Reported 



Crepis — Old World 



Species 



Somatic 

chromosome 

number 



Number 
of plants 
examined 



Accession 



Subgenus 



*C. albida asturica (Lacaita 
et Pau) 

C. albida macrocephala 
(Willk.) 

C. alpestris (Jacq.) Tausch. 

C. argolica Babe 

C. argolica tirynica Babe 

C. aspera jordanensis Babe. 

C. aurea lucida (Ten.) 

C. bellidifolia Loisel 

C. bhotanica Hutchinson 

C. bifida (Vis.) F. et M 

C. bithynica Boiss 

C. canariensis (Sch. Bip.).... 

C. clausonis Pomel 

\C. crocea (Lam.) 

C. divaricata (Lowe) F. 
Schultz 

C. eigiana Babe 

C. eritreensis Babe 

C.flexuosa (DC.) Benth. et 
Hook.f 

C.fonliana Babe 

C.fuliginosa S. et S 

C. granatensis Babe 

%C. hieracioides Lowe 

C. hyemalis (Biv.) C. P. et 
G 

C. hypochaeridca rhodesica 

Babe 

1C. juvenalis (Delile) F. Sch 

C. kashmirica Babe 

C. multicaulis congesta 

(Rgl.) 

C. mungieri Boiss 

C. myriocephala Coss. et 

DR. in forms 

C. nigricans Viv 

C. oreades Schrenk 



10 

10 

8 

8 

8 

8 

10 

8 

16 

10 

10 

8 

8 

16 

8 

8 

10 

14 

8 
6 



12 

10 
12 

16 



2 
2 
2 
3 
3 
2 
1 
2 
6 
3 
3 
4 
6 
*z 

4 
4 
1 

2 
3 
11 
4 
5 



2088 

2957 

2512 

2884 

3036 

3010 

2912 

2921 

3216, 3245 

3057, 3083, 3084, 3087 

3218 

3049 

2848 

2174, 2352, 2353 

2980 

3125, 3138 

3005 

2983 

3225 

2994, 3043, 2891 

1894 

2817,2818,2823 

3053 

3059 

3205, 3206, 3207 

3186 

3187 

2870, 2876, 2877 

2844, 2845 

3020 

2981 



B 
C 
E 
E 
B 
C 
B 
C 
E 
E 
B 
B 
C 

B 
E 
B 

E 
B 
E 
E 
B 



C 
B 
C 

E 

E 

B 
B 
B 



* Cf. C. asturica (Hollingshead and Babcock, 1930). 
t Cf. C. bungei 2174 (Hollingshead and Babcock, 1930). 
} One triploid plant. 
1 One trisomic. 



1934] Babcoclc-Cameron : Chromosomes and Phylogeny in Crepis. II 289 

TABLE 1— {Concluded) 



Species 



C. patula Poiret 

|l C. polytricha Turcz 

C. pterothecoides Boiss 

C. pumila (Lowe) 

C. pygmaea L 

C. raulinii Boiss. 

C. reuteriana fa. hirta Babe. 

C. roberlioides Boiss 

C. sancta beirutica Babe 

C. selosa to paliana Babe. 

C. stojanovii T. Georg 

C. suberostris Batt 

C. suffreniana (DC.) Lloyd 
C. taraxacifolia laciniala 

(Lowe) 

C. taraxacoides Desf 

C. taygetica Babe 

C. thomsonii Babe. 

C. triasii (Camb.) Fries 

C. tubaeformis Halacsy 

C. vesicaria L. 4n forms 



C. viscidula Froel 

C. willemetioides Boiss. 



Somatic 

chromosome 

number 



16 



12 
10 



10 



10 



16 
40 
10 



16 

12 
12 



Number 
of plants 
examined 



Accession 



2839. 

2562. 

3232 

3022. 

3251.. 

2875.. 

3134 

3129 

3160 

2906 

3176 

2829 

2975. 



2803,2815,2819 

2944 

2893 

3208 

2945,2949 

3066,3069 

2851,2852,2853,2854, 
2947, 2948, 3056, 3203 

3178 

3217 



Subgenus 



Lactuca depressa (Hook. f. et 
Thorn.) (Crepis depressa) 

Prenanthes glomerata Dene. 
(Crepis glomerata Benth. 
et Hook, f.) 



16 



16 



E 
C 
E 
B 
E 
E 
E 
E 
E 
B 
E 
B 
B 

B 
B 
E 
B 
B 
E 
B 

C 
E 



Crepis — American 


C. atribarba A. A. Heller 


88? 


2 


3045 


E 








Other Genera 



|| Ci. C. polytricha (Baboock and Navashin, 1P30). 

Root-tips for this study were fixed in chrom-acetic-formalin solution 
1, as described on page 3, Hollingshead and Babcock (1930). Paraffin 
sections were cut from 8 to 12/j. thick and stained either in Heidenhain's 
iron haematoxylin or crystal violet. A Zeiss 1.3 oil immersion objective 
and Zeiss compensating ocular were used throughout this study. Draw- 
ings were made with a camera lucida at a magnification of 3750 and 
reduced to 2500 in reproduction. In all other respects a procedure was 
adopted which would produce results comparable with those reported 
by Hollingshead and Babcock (1930). 



290 University of California Publications in Agricultural Sciences [Vol. 6 



CHROMOSOME NUMBERS 

The chromosome numbers of sixty-eight species of Crepis have already 
been reported. In table 1 are given the diploid numbers of forty species, 
nine subspecies, and several forms not previously reported. One sub- 
species is relisted because of a change in nomenclature; and one species 
(polytricha) appears here because it was not reported in the first paper 
of this series. The species commonly known as Crepis glomerata was 
excluded from Crepis by Babcock and Navashin ( 1930) . This species has 
been referred to Prenanthes, where it was originally classified by its 
author. Another species, long known as Crepis depressa, has been re- 
ferred to Lactuca. These two excluded species are listed at the end of 
table 1 for purposes of record. Classification of the Crepis species accord- 
ing to subgenus is shown in table 1, right-hand column; C = Catonia, 
E = Eucrepis, B = Barkhausia. 



CHROMOSOME NUMBER AND PHYLOGENY 

The Subgenera 

In earlier publications four subgenera have been recognized, namely, 
Paleya, Catonia, Eucrepis, and Barkhausia. More recent studies show 
that the four species previously classified in Paleya are primitive rep- 
resentatives of Catonia and Barkhausia, therefore the subgenus Paleya 
has been merged with the two just mentioned. This makes possible a 
more satisfactory representation of phylogenetic relations. 

In order to discuss the bearing of chromosome number on phylogeny, 
it is necessary first to consider the relationships of the three subgenera 
as determined from other evidence. It is not proposed to present all this 
evidence in detail here but merely to indicate the general situation as 
clearly as possible. In addition to the number of species in each sub- 
genus, their duration of life (whether perennials or annuals and bien- 
nials), and their geographic distribution, certain aspects of their com- 
parative morphology have been found especially valuable. The morpho- 
logical characters used in differentiating the subgenera are presented 
most readily in the form of an analytical key. 

KEY TO THE SUBGENEEA 

Bracts of the mature involucre unchanged or merely indurate Catonia 

Bracts of the mature involucre dorsally keeled or spongy-thickened 

or both. 

Achenes unbeaked or only very shortly or coarsely beaked (rarely 
with beak equal to body) Eucrepis 

Achenes definitely beaked; the beak usually long and slender Barkhausia 



1934] Babcock-Cameron: Chromosomes and Phytogeny in Crepis. II 



291 



Without going into details or pausing to discuss certain exceptional 
species which are difficult to classify according to the foregoing scheme, 
it is obvious that there is progressive specialization in the structure of 
both involueral bracts and achenes. Along with this increasing special- 
ization there is a definite trend toward reduction in length of life. Thus, 
all Catonia species are perennial; while one-fourth of the Eucrepis and 
three-fourths of the Barkhausia species are annual. The evidence from 



CATONIA 

45 SPECIES 
OLD WORLD 
PERENNIALS 



EUCREPIS 

120 SPECIES 
105 OLD WORLD 
15 NO. AMERICAN 
90 PERENNIALS 

30 ANNUALS 



BARKHAUSIA 

45 SPECIES 
MEDITERRANEAN 
AND ADJACENT 

REGIONS 
II PERENNIALS 

34 ANNUALS 




Fig. 1. Composition and phylogenetie status of the subgenera of Crepis. 

geographic distribution will not be presented here; in general it is in 
agreement with the inference that Catonia is the most primitive, and 
Barkhausia the most recent group, while Eucrepis is intermediate. 
Furthermore, there are a number of border-line species in Eucrepis, 
some of which verge toward Catonia and others toward Barkhausia. 
Thus, the general situation in respect to phylogenetie relations between 
the subgenera may be represented as in figure 1. 

Chromosome numbers in the subgenera. — The distribution of chro- 
mosome numbers in the three subgenera is shown in figure 2. An ex- 
ponent indicates the number of species having a given chromosome 
number. This representation reveals several significant facts. It will be 
noted that the entire series of chromosome numbers is found in Eucrepis, 
while Catonia and Barkhausia have comparatively small series. But in 
each subgenus, as here represented, there is more than one basic number. 



292 



University of California Publications in Agricultural Sciences [Vol. 6 



The basic numbers common to all three subgenera are 8 and 10, there 
being fifty-five species with eight, and nineteen species with ten chro- 
mosomes. In Catonia and Eucrepis there is a third basic number, namely, 
12, and in Eucrepis, a fourth, namely, 14. But as will be shown, these 
"basic" numbers are not all equally primitive. Furthermore, the subgen- 
era may contain more than one phylogenetic line of a given basic number. 



CHROMOSOME NUMBER AMD PHYLOGENY 
IN CREPIS 



EUCREPIS 
44 2 55? 88? 2 

22 5 (15-24) 40 
CATONIA / 40 2 ^ \l6/6 2 

j 6 3 , 4 3 , 2 7 7 6 8 25 

|2 3 I0 3 8 8 



BARKHAUSIA 
I6 2 ? (10-18) 




Fig. 2. Distribution of chromosome numbers in the subgenera 
in relation to phylogeny. 

The great predominance of 8-chromosome species has led to the erro- 
neous assumption by some writers that eight is the most primitive num- 
ber in Crepis. But frequency of occurrence is not a sufficient basis for 
such an inference. The important fact that some of the 8-chromosome 
species are more highly specialized than any 10-chromosome species has 
been overlooked. Of still greater significance is the fact that none of 
the 8-chromosome species, even in Catonia, are as primitive in morpho- 
logical aspects as are some of the 10-chromosome species, such as sibirica 
and pontana in Catonia, raulini and bithynica in Eucrepis, and albida 



1934] BabcocJc-Cameron : Chromosomes and Phylogeny in Crepis. II 293 

in Barkhausia. The 12- and 14-chromosome species present special prob- 
lems which will be considered later. As between 8 and 10 the latter must 
be considered the more primitive number in Crepis or the progenitors 
of Crepis; but in the present representation 8, 10, 12, and 14 are all 
treated as basic numbers. 

The diagram (fig. 2) also shows the comparative amount of differen- 
tiation in chromosome numbers in the three subgenera. In Catonia all 
the species have basic numbers except three, two of which certainly, and 
the third (bhotanica) probably, were derived from 8-chromosome an- 
cestors. Predominance of basic chromosome numbers in this subgenus 
is associated with persistence of primitive morphological features. In 
Barkhausia, however, we have the most highly specialized portion of the 
genus. Yet all but three of the species thus far studied have the basic 
number 8 or 10. This immediately suggests the inference that the higher 
degree of specialization which is characteristic of Barkhausia has devel- 
oped chiefly through other evolutionary processes than those involving 
changes in chromosome number. One such process, as has already been 
pointed out (Babcock and Navashin, 1930), is factor or point mutation 
(genovariation). 

The greatest diversity in chromosome numbers occurs in Eucrepis 
and several different processes of alteration in chromosome number have 
been involved. From species with eight chromosomes there have been 
derived species with six by loss of one pair; species with sixteen by 
autotetraploidy; a species with fifteen, twenty, and twenty-four which 
seems to have arisen through amphidiploidy; polyploids with about 
forty. Species with eight and fourteen chromosomes respectively are be- 
lieved to have hybridized and produced amphidiploids with twenty-two; 
and a polyploid series has been derived from the last. At the same time 
there are various degrees of specialization which may have been made 
possible largely by gene mutations. 

Catonia 

The phylogenetic relations of seventeen species of Catonia, as deter- 
mined primarily from gross morphology, geographic distribution and 
chromosome number, are shown in figure 3. It must be admitted that the 
evidence from chromosome morphology, to be presented below, has also 
been considered in arranging this diagram; also the indications of rela- 
tionship to be found in natural and artificial hybrids between species. 
In C. blattarioides, for example, gross morphology alone seems to con- 
nect it more closely with sibirica and pontana than with alpestris and 
hypochaeridea, but the evidence from chromosome number and morphol- 
ogy and the occurrence of natural hybrids between blattarioides and 
alpestris, seem to outweigh the evidence from superficial appearance. In 



294 



University of California Publications in Agricultural Sciences [Vol. 6 



general, however, the degree of morphological resemblance is roughly 
indicated by this diagram. 

The 5-paired species, especially sibirica and pontana, are in several 
respects among the most primitive morphological types in the entire 
genus, while aurea, particularly subsp. lucida, exhibits the greatest re- 

CATONIA 

PHYLOGENY AND CHROMOSOME NUMBER 



AUREA IO v 



HOOKERIANA 8 



PONTANA 10 
SIBIRICA 10 



VISCIDULA 12 
PALUDOSA 12 




C0NY2AEF0LIA 8 



BHOTANICA 16 



KASHMIRICA 12 



Tig. 3. Phylogenetic relations and chromosome numbers 
of seventeen species in subgenus Catonia. 

duction in size of the whole plant and all its parts to be found in the 
Catonia species thus far studied cytologically. 

The 4-paired Catonia species fall into two main groups and they may 
represent two or three different progenial stocks. On the left are shown 
the three species already mentioned and C. hookeriana, which is suffi- 
ciently like hypochaeridea to suggest that it diverged from the same 
stock. On the right are six species, conyzaefolia-crocea, which are evi- 
dently related and which may have sprung from the same stock as the 
4-paired species on the left. The evidence for derivation of crocea from 



1934] Bab cock-Cameron: Chromosomes and Phylogeny in Crepis. II 295 

bungei will be given below. Both crocea and polytricha are certainly 
polyploids with n = 4 as the base number. C. bhotanica is a prominent 
species with sixteen chromosomes, which shows sufficient resemblance 
to those just above it in the diagram to warrant the assumption that it 
arose from the same 4-paired ancestral line; but our study of chro- 
mosome morphology has not gone far enough to demonstrate conclu- 
sively that it is a polyploid with n = 4 as the base number. 

The 12-chromosome Catonia species certainly represent two widely 
divergent lines, which differ greatly from each other morphologically 
as well as from all other species in the genus. On the extreme left are 
paludosa and viscidula which, in habit and fruit characters, show some 
resemblance to Eieracium species. Apparently they represent a rather 
stable primitive stock, because few if any other distinct species are 
known to belong in this group, although paludosa is one of the most 
widely distributed species in the genus. On the extreme right is kash- 
mirica, which has long been confused with blattarioides although the 
resemblance is merely superficial. There is still some question whether 
these three 12-chromosome species are diploids or polyploids of some 
sort. The haploid number may be 3 or 6. 

Eucrepis 

Fifty-nine species of Eucrepis are arranged in figure 4 according to 
phylogeny and chromosome number. Here again chromosome morphol- 
ogy has been considered together with other available criteria of rela- 
tionship; and the degree of resemblance in gross morphology is roughly 
indicated by the arrangement of groups and within groups. In general 
the more primitive species are below and the more specialized forms 
above, with the exception of the two perennials, oreades and robertioides, 
which appear above biennis and ciliata, and the ten American species 
which are placed at the top because they are probably of comparatively 
recent origin. 

The species having 4 as the haploid number are all on the left side of 
the diagram except the oreades-suffreniana assemblage on the upper 
right. Of all the 8-chromosome Eucrepis species, patula is in certain 
respects the most primitive and it has no close relatives. But the pan- 
nonica series of perennials and the argolica group of annuals were prob- 
ably derived from an ancestral stock represented by patula, which is 
apparently a relict in which certain parts, especially the pappus, have 
become very greatly reduced. Pannonica, lacera, and chondrilloides are 
closely related and fairly primitive species, while incana and taygetica 
are polyploids showing considerable resemblance to them. The argolica 
quartet is a very closely related group in which the marked differentia- 
tion in gross morphology must have come about through gene mutation. 



296 



University of California Publications in Agricultural Sciences [Vol. 6 



On the other side of patula are tenuifolia and the gymnopus-pt erothe- 
coides group. Evidence that tenuifolia has 4 as the hasic haploid number 
will be presented under chromosome morphology. This species is the 

EUCREPIS-PHYLOGENY AMD CHROMOSOME NUMBER 



MONTICOLA 55? 

SCOPULORUM 44 ?\ 

OCCIDENTALS 22. 44\ 



^ATRIBARBA 88? 
f^BARBIGERA 88? 
LaCUMINATA 33.44. 55? 
LGRACILIS 22.55? 




ANDERSONII ZZ 
GLAUCA ZZ 
RUNCINATA 22 



AMPHIDIPLOID HYBRIDS ZZ 

k 
PTEROTHECOIDES 8 ! LEONTODONTOIDES 10 



PULCHRA 8 

GRAWATENSIS 8 

PALAESTINA 8 

MULTIFLORA 8 
DIOSCORIDIS 8^1 
TUBAEFORMIS 8 
ARGOLICA 8 



TAYGETICA 40 
IIMCANA 16 



CHONDRIL- 
LOIDES 8 

LACERA 8 
PANNONICA 8 




SUFFREWIAIMA 8 
AJEGLECTA 6.8 
PARVIFLORA 8 
CAPILLARIS 6 
TECTORUM 8 
NICAEEWSIS 8 

ROBERTIOIDES 8 
OREADES 8 

CILIATA 40 
BIENNIS 40 

HIEROSO- 
LYMITANA 12 

WILLEMETI- 
OIDES 12 



MUNGIERI 

MONTANA 

PYGMAEA 

LYRATA 

MOLLIS 



FLEXUOSA 14 

ELEGANS 14 

NANA 14 



Fig. 4. Phylogenetic relations and chromosome numbers 
of fifty-nine species in subgenus Eucrepis. 

only representative, thus far studied cytologieally, of an eastern Asiatic 
group which was probably derived from a 4-paired stock different from 
the patula line. At any rate, that the two lines have diverged widely is 



1934] Babcock-Cameron : Chromosomes and Phytogeny in Crepis. II 297 

shown not only by gross morphology but also by geographic distribution, 
since the known representatives of the patula line are all restricted to the 
Mediterranean region. 

The gymnopus-pterothecoides series is a remarkable group of related 
species in which reduction in life-cycle and morphological specialization 
has proceeded without change in chromosome number and without much 
change in chromosome morphology, as will be shown below. The lower 
five species in this series are perennials with relatively unspecialized 
fruits; while the upper five are annuals which are all more specialized, 
especially in fruit characters, than the perennials. The most extreme 
example of such specialization is found in pterothecoid.es, in which the 
achenes are shortly beaked and this plant, unlike all the others, is very 
precocious and short-lived. These ten species, therefore, provide a beau- 
tiful example of an evolutionary series in which, by elimination, it 
must be concluded that the genetic process making evolution possible is 
gene mutation. The problem of derivation of this interesting group, 
however, involves the possibility of transformation in chromosome num- 
ber from 10 to 8. This will be discussed under chromosome morphology. 
For the present it is sufficient to indicate by the broken lines and ques- 
tion marks that the group may have come from either a 4-paired or a 
5-paired progenial stock. 

The oreades-suffreniana assemblage, with n = 4 for base number, as 
treated here, also involves hypothetical derivation from a stock with 
n = 5 as base number. This hypothesis is supported by two lines of evi- 
dence. First, biennis with about forty chromosomes has been proved by 
cytogenetic study (Collins and Mann, 1923) to be an octoploid species 
and its close relative, ciliata, has the same number of chromosomes. 
Second, nicaeensis, with eight chromosomes, is a biennial species and 
is so similar in general appearance to biennis as to make it difficult for 
anyone but an experienced student to identify herbarium specimens of 
the two species. The annual species, tectorum, also shows considerable 
resemblance to nicaeensis and biennis, and the other four annuals, capil- 
laris, parviflora, neglecta, and suffreniana, are progressively farther 
removed. The alpine perennials, oreades and robertioides, each with 
eight chromosomes, are thought to be more primitive representatives 
of the same 4-paired stock that produced the nicaeensis group. 

The 10-chromosome Eucrepis species appear in the central part of 
the diagram. Only eight such species have been reported thus far, but 
there are several related species which have not been available for 
cytologic study. These eight species comprise three diverse groups 
which probably represent different lines in the immediate ancestry 
although these lines converge and probably originated in a common pro- 
genial stock. The most primitive group contains raulinii and bithynica, 
which are alpine perennials with a woody caudex as in the 4-paired 



298 University of California Publications in Agricultural Sciences [Vol. 6 

species, oreades and robertioides; this fact gives added weight to the 
hypothesis that the latter originated from a 5-paired ancestral stock. 

The multicaulis and saucta-bifida assemblage is extraordinarily inter- 
esting in that sancta and bifida represent a group of about ten species 
which have hitherto been classified under the genus Pterotheca although 
Hooker (1882) expressed the opinion that this group should be merged 
with Crepis. Since the one character supposed to distinguish Pterotheca 
from Crepis (bristle-like paleae on the receptacle) is sometimes absent, 
Hooker's opinion appears to be sound, and now that evidence both 
morphological and cytological establishes the relationship of these two 
species with Crepis multicaulis this opinion is confirmed. The question 
of relative position in the phylogenetic series is somewhat complicated. 
Sancta and bifida, because of their annual habit and dimorphic fruits, 
would be considered more specialized than multicaulis; but reduction 
in size of flowers and fruits has gone much farther in multicaulis. The 
position of these three species as represented in figure 4 is largely a 
matter of convenience. 

Crepis tingitana, a native of Morocco and Spain, is in certain respects 
a primitive species. At any rate it shows strong resemblance to certain 
African species of Catonia. In shape of achenes, however, it is variable, 
certain forms having the achenes definitely though coarsely beaked. 
Prom external morphology alone it would seem unlikely that tingitana 
arose from the same 5-paired stock as the preceding species. At the same 
time it shows sufficient resemblance to suberostris and leontodontoides 
to warrant the inference that they may have arisen in the same ancestral 
line. But the two latter species are more highly specialized, particularly 
suberostris, which is an annual; while both include forms with Bark- 
hausia-\ike achenes. 

The seven 6-paired species comprise a well marked yet much diversi- 
fied group. C. mollis is evidently the most primitive; then come lyrata 
and pygmaea; then the two pairs of closely related species, montana and 
mungieri, willemetioides and hierosolymitana. There are no closely re- 
lated groups, so it appears that they arose from a distinct ancestral 
stock. But certain peculiarities in the morphology of their chromosomes 
remain to be considered. 

The three 7-paired Eucrepis species, nana, elegans, and flexuosa, are 
also closely related to one another and seem to have arisen from a dis- 
tinct ancestral stock. There are good reasons for thinking that these 
low-growing perennials are some of the remaining representatives of a 
comparatively ancient group. In fact, the most diminutive one, C. nana, 
is also the most widely distributed species in the entire genus, extending 
from central Asia across the northern hemisphere to northeastern North 
America. Such evidence as this lends support to the hypothesis which 
has been advanced (Hollingshead and Babcock, 1930) that 7-paired 



1934] Babcock-Cameron : Chromosomes and Phylogeny in Crepis. II 



299 



species must have hybridized with certain 4-paired species and produced 
through amphidiploidy the 22-paired American species and their poly- 
ploid relatives shown at the top of figure 4 (cf. fig. 156) . 

Barkhausia 

The phylogenetic relations of thirty-two species of Barkhausia and their 
chromosome numbers are shown in figure 5. In general the most primi- 



BARKHAUSIA 

PHYLOGENY AND CHROMOSOME NUMBER 



HACKELII 16 
TARAXACIFOLIA £ 
LYBICA 8, 
HYEMALIS 8. 
CLAUSONIS 8. 
TRIASII 8. 
HIERACIOIDES i 
DIVARICATA 8. 
CANARIENSIS 8^ 
FONTIANA 8 



MYRIOCEPHALA 8 
MARSCHALLII 8 




SENECIOIOES 8 

NIGRICANS 8 

THOMSON 1 1 10 

| ERITREENSIS 10 
FOETIDA 10 
COMMUTATA 10 

RUBRA 10 
ALPINA 10 
SYRIACA 10-18 
ALBIDA 10 



Fig. 5. Phylogenetic relations and chromosome numbers 
of thirty-two species in subgenus Barkhausia. 

tive species are near the base and the most specialized at the top. The 
species having ten chromosomes, shown on the right, include one per- 
ennial, C. albida, of southwestern Europe and Morocco, which consists 
of six subspecies and which is one of the most primitive specific groups 
in the entire genus. There is good morphological evidence of its fairly 
close relationship to C. alpina of Asia Minor, and the associated species, 
C. syriaca; also, though less closely, to C. rubra of southern Europe; 



300 University of California Publications in Agricultural Sciences [Vol. 6 

while farther removed but still clearly connected is the commutata- 
thomsonii group of southern Europe, Asia Minor, northeast Africa, 
Persia, and India. Allied with the latter, especially with C. thomsonii, 
is the 8-chromosome species, C. bureniana. The morphological evidence 
of this relationship is indisputable. The question of chromosome morph- 
ology is discussed below. 

The 8-chromosome Barkhausia species include three distinct series 
which seem to have a common origin. Below on the left are four peren- 
nial species, fontiana of western Morocco, canariensis of the Canary 
Islands, and divaricata and hieracioides of Madeira. They exhibit con- 
siderable morphological similarity. Fontiana and canariensis especially 
must be recognized as fairly primitive types of Barkhausia. Next to these 
is the triasii-myriocephala assemblage of the Mediterranean Islands and 
bordering countries. Of these, triasii, clausonis, hyemalis, and some 
forms of vesicaria are perennials, while the others are annuals which 
sometimes behave as perennials under favorable conditions. C. myrio- 
cephala is unquestionably the most specialized member of this series 
through reduction in size of flower heads, florets, and fruits, although 
the plant and its basal leaves are very large. The assumed derivation of 
hackelii from taraxacifolia and of taraxacoides from vesicaria is con- 
sidered in connection with chromosome morphology. 

The remaining series of 8-chromosome Barkhausia species, all of the 
Mediterranean littoral, are annuals except bellidifolia and bursifolia, 
which, although rather specialized through reduction in size of plant, 
flowers, and fruits, have retained the perennial habit. C. juvenalis, 
aculeata, and amplexifolia are obviously closely related, being char- 
acterized by having two distinct types of achenes which are similar in 
all three species. C. aspera and C. setosa also have dimorphic achenes, 
but they differ from each other and from the juvenalis group in im- 
portant characters of the fruits. The two remaining species, nigricans 
and senecioides, are most highly specialized through reduction through- 
out the whole plant. They are very precocious, short-lived annuals. 

CHROMOSOME MORPHOLOGY 

The general aspects of chromosome morphology in Crepis have been 
discussed in earlier publications (cf. Hollingshead and Babcock, 1930; 
Babcock and Navashin, 1930). The existence of comparable pairs of 
chromosomes in different Crepis species was first noted by Navashin 
(1925) and designated as follows: A, long chromosome with longest 
proximal arm; B, long chromosome with next longest proximal arm; 
C, usually a shorter chromosome with shorter proximal arm, but some- 
times there is little difference between B and C; D, satellite-bearing 
chromosome; E, a shorter chromosome with median constriction. In the 



1934 J Babcock-Cameron : Chromosomes and Phylogeny in Crepis. II 301 

following illustrations the same order of arrangement of the members 
of the haploid genom has been followed throughout. This order, from 
left to right, is A, B, C, D, E, in 5-paired species. Diploid species with 
more than five pairs often have two or more pairs of E chromosomes, 
but sometimes B or C seems to be duplicated. The 4-paired species lack 
E ; the 3-paired species, capillaris, lacks B ; the other 3-paired species, 
fuliginosa, lacks C. 

Catonia 

Cytological studies have been completed on fifteen of the seventeen 
species represented in figure 3. The haploid genoms of the three 5-paired 
species and of two of the 6-paired species are shown in figure 6. In the 



w 



aurea 



Kill 

pontana 



rn i> i 



viscidula 



\mv 



paludoea 



sibirica 

Fig. 6. Species of Catonia with n = 5 and 6. 

former a fairly close resemblance between sibirica and pontana will be 
seen in all five chromosomes, the chief difference being in the length of 
the proximal arms of A and B. This close correspondence is in agreement 
with the morphological evidence that these species are among the most 
primitive of the genus, although distinct in many characters and occu- 
pying widely separated geographic areas. The genom of aurea differs 
strikingly, all the chromosomes being smaller and the C having a very 
short distal arm. Aurea is a more recent species, since it exhibits spe- 
cialization through reduction in size and in the strongly attenuate 
achenes and the development of much red color in the flowers. 



302 University of California Publications in Agricultural Sciences [Vol. 6 

The two 6-paired species are of special interest for several reasons. 
They are closely similar, yet unquestionably distinct in numerous char- 
acters. Paludosa is the most widely distributed species of Catonia, while 
viscidula is restricted to the northern Balkan states. Furthermore, 
paludosa is more reminiscent of Hieracium in habit, habitat, achene 
shape, and the yellowish brittle pappus than any other species which has 
been studied cytologically. Yet the number, 12, has not yet been re- 
ported in Hieracium. These two species therefore appear as one of 
several small groups which may justifiably be included within Crepis, 
but which verge more or less definitely toward some other genus. Since 
12 is not known to occur in Hieracium one may fairly question whether 
it must be looked upon as a primitive number in Crepis. Possibly these 
two 6-paired species were derived from some 5-paired stock. Further 
study is needed on these two species and on kashmirica in order to solve 
this problem. 

The eight 4-paired species of Catonia fall naturally into two groups 
according to chromosome morphology, as is shown in figure 7, and by 
comparing this with figure 3 it will be seen that this grouping agrees 
with the arrangement according to morphology, geographic distribu- 
tion, and the occurrence of natural hybrids. The close correspondence 
between the chromosomes of blattarioides and alpestris is the more 
remarkable in view of the marked morphological differences between 
these two montane species of southern Europe. C. alpestris also occurs 
in Asia Minor, which adds weight to the assumption that it had a com- 
mon origin with C. hypochaeridea of South Africa. The hypochaeridea 
genom has a strong resemblance to that of alpestris and there is a gen- 
eral morphological resemblance between the two plants. The Moroccan 
C. hookeriana, a plant of the Grand Atlas Mountains, also resembles C. 
alpestris, though less closely than hypochaeridea, and its chromosomes 
differ more, especially B and C. From the size of the chromosomes it 
would appear that these four species are of approximately equal age. 
The slightly smaller size in hypochaeridea is in agreement with the evi- 
dence from geographic distribution that it is somewhat more recent than 
the other three. 

Strong similarity in size and shape also appears in the genoms of 
cony zae folia, a species distributed from southern Europe to central 
Asia, and of burejensis and chrysantha of eastern Asia. The three are 
similar morphologically, as are their genoms, but burejensis is slightly 
more specialized than conyzaefolia, and chrysantha is much more re- 
duced throughout. C. polytricha has been confused with C. chrysantha, 
from which it is easily distinguished by the larger, ventricose involucre 
and yellow indumentum and by other characters. Critical study of the 
chromosomes of polytricha has been difficult because of limited material. 
From available evidence it appears almost certain that this species is 



1934 j Babcock-Cameron : Chromosomes and Phylogeny in Crepis. II 



303 



an autotetraploid, but the marked differences between polytricha and 
chrysantha in the A and D chromosomes indicate that if polytricha did 
originate from chrysantha through polyploidy, the event was not of 
recent occurrence. This is consistent with the morphological differences 
between the plants and the wide geographical distribution of polytricha. 



hooker I ana 



hypochaeridea 



n 



alpestris 



polytricha 



10 r Pi) 



chrysantha 



mi 



bure jensls 



blattarloides J 

conyzaefolla 
Tig. 7. Species of Catonia with n — 4 and 8. 

Genoms of C. bungei and C. crocea of Catonia are shown in figure 8 in 
comparison with that of C. oreades of Eucrepis. Morphologically, C. 
crocea is either intermediate between the two diploid species or exceeds 
them both in certain quantitative characters. The geographic distribu- 
tion of the three species is in excellent agreement with the hypothesis 
that crocea originated as an amphidiploid hybrid between the other two. 
Genetic evidence is limited to data on some F x hybrids between bungei 



304 University of California Publications in Agricultural Sciences [Vol. 6 

and erocea. These hybrids were intermediate between the two species 
and exhibited a low degree of fertility. Chromosome morphology agrees 
fairly well with the foregoing hypothesis, although the chromosomes of 
oreades and bungei are too similar to make the evidence definite. In ar- 
ranging the haploid genom of erocea, in each of the four sets of two 
chromosomes the one believed to correspond with bungei is shown on the 



no 



oreadea 



WOicd 



erocea 



litl 



bungei 
Fig. 8. Cytological evidence on the origin of Crepis erocea. 

left. The absence of a satellite from the "oreades" D chromosome in 
erocea seems to be constant — another example of amphiplasty (Nava- 
shin, 1928). 

EUCBEPIS 

The genoms of the 10-chromosome Eucrepis species are presented in 
figure 9. It will be recalled that raulinii and bithynica are rather primi- 
tive types which may have arisen from the same 5-paired ancestral line 
as the other six species. The close correspondence in shape among all 
eight genoms agrees with this conception. The full significance of this 
evidence can hardly be appreciated without a somewhat detailed com- 
parison of the morphology of the plants (pp. 297 f .) . The high degree of 
reduction and specialization which has taken place in the midticaulis 
group seems to have been accompanied by notable reduction in size of 
the chromosomes. Tingitana also is a rather primitive species, while 



1934] Babcock-Cameron : Chromosomes and Phylogeny in Crepis. II 305 

leontodontoides is much more specialized in several characters. Here 
again there is notable difference in size of the chromosomes. Suberostris, 
however, seems an exception to the general rule since its chromosomes 



rccji 



bifida 



1M>< 



leontodontoides 



sancta • ^ w 



suberostris 



n«it fciu 



multicaulis 



ting! tana 



fr>H 



blthynica 



WO* 

raulinil 
Fig. 9. Species of Eucrepis with n = 5. 



are large, although it is a considerably reduced annual. In fact it fits less 
well in this series than the other species, not only with reference to its 
chromosomes, but also in its external morphology; but it has no closer 
relatives. 



306 University of California Publications in Agricultural Sciences [Vol. 6 

Crepis patula and its nearest relatives are represented by the haploid 
groups of chromosomes shown in figure 10. That the relationship is not 

tlflKH 101 

incana multiflora 

chondrilloides dioscoridla 

mi rm 



lacera 



w\ 



pannonica 



tubaef ormi9 



no 



argolica 



no 



patula 
Fig. 10. Species of Eucrepis with n = 4. 

close is indicated by the fact that the patula genom does not correspond 
entirely with the chromosome types in either of the two series. It is note- 
worthy, however, that the B chromosome in patula corresponds with B 



1934] Babcoclc-Cameron : Chromosomes and Phylogeny in Crepis. II 307 

in the argolica series, while patula C is more like C in the pannonica se- 
ries. This may indicate a common ancestry and is in keeping with the 
evidence that patula is really an old species which is still primitive 
in the greater number of characters but has become greatly reduced 
in a certain part. It is not unlikely that, in its comparatively long exist- 
ence as a species, there has also been some reduction in the size of its 
chromosomes. 

The close similarity of the pannonica, lacera, and chondrilloides ge- 
noms is to be expected from their common morphological features. It 
may be noted that chondrilloides is the most restricted in distribution 
and the most specialized of the three, and that its chromosomes appear 
to be slightly though perhaps not significantly smaller. That incana is an 
autotetraploid appears fairly certain from its B, C, and D chromo- 
somes, and the apparent unlikeness in the A's may not be an actual dif- 
ference. The diploid species from which it may have originated has not 
yet been discovered. C. taygetica may be mentioned here as another 
polyploid species, of which the diploid ancestor is unknown. Evidence 
from morphology and geographic distribution places it in this series. 
Incomplete study of its chromosomes indicates that it is a high poly- 
ploid of some sort, possibly a decaploid. The presence in somatic tissue 
of forty chromosomes which correspond in size to those of other species 
in this group lends considerable weight to this assumption. Only three 
chromosomes were observed which bore unmistakable satellites, but sev- 
eral others were present which might be D chromosomes and it is fre- 
quently found that, in a large genom such as this, all the D's do not pos- 
sess a satellite. The argolica series of very closely related species from 
Greece also exhibit great uniformity in chromosome types. The only 
point of importance is the inconsistency with the general rule that more 
highly specialized and reduced species have smaller chromosomes, since 
multiflora is such a species, while argolica is certainly the most primi- 
tive of the four. 

Crepis tenui folia was reported by Hollingshead and Babcock (1930) 
as having fifteen chromosomes. This report was based on eight plants, 
grown from wild seed, of one accession from Mongolia. Since then we 
have counted the chromosomes of thirty-three plants, grown from wild 
seed, of a different accession also from Mongolia. Of these, thirty-one 
had fifteen chromosomes and two had twenty-four chromosomes as the 
diploid number. It appears that most Mongolian plants of this species 
have fifteen chromosomes, the odd number being maintained through 
some form of apomictic reproduction, but that sexual reproduction oc- 
casionally takes place, producing plants with higher numbers. More 
recently an accession of this species has been received from Kashmir, 
which has 2n — 20. In figure 11a is shown a diploid group with fifteen 
chromosomes, and b is the haploid genom in which each of the eight 



308 University of California Publications in Agricultural Sciences [Vol. 6 

types represents a pair except the one at the right end, which is the odd 
member. It will be noted that there are two pairs of A's, B's, and D's in 
the diploid complex. Figure lie, d presents the haploid genom of the 
Himalayan form of the species, in which each type shown in c repre- 
sents a pair and the four chromosomes in d are odd. Referring to the 
haploid genom, there are certainly two types of D chromosomes and 



TAff 



Fig. 11. Crepis tenuifolia: a, diploid genom of the 
15-chromosome form; b, one member of each of the 
seven pairs in diploid genom and, at the right end, 
the odd chromosome ; c, one member of each of the 
eight pairs in a 20-chromosome form; d, the four odd 
members in the same genom. 

presumably also of A's, B's, and C's or E's. Hence it appears certain 
that the species originated as an amphidiploid hybrid and that the odd 
number, 15, is maintained by some form of apomictic reproduction, al- 
though sexual reproduction sometimes occurs producing such forms as 
the 24-chromosome plants already mentioned. The 20-chromosome form 
may also be a segregation product resulting from sexual reproduction. 
Further studies are in progress on this remarkable species. 



1934] Babcock-Cameron: Chromosomes and Phytogeny in Crepis. II 309 

In figure 12 are depicted the highly uniform genoms of the ten species 
in the gymnopus-pterothecoides series. The rather wide morphological 

reuteriana 



praemorsa 



-IK* 



pterothecoidea 



*W 101 

eigiana ™ 9 



pulchra 



4K) -,)f| 

incarnata ^^ *w w 

granatensis 

0)d 



051) 



palaestina 



nm 



gymnopus stojanovll 

Fig. 12. Species of Eucrepis with n = 4. 

differences among the members of this group must depend upon genie di- 
versity. The extent of some of these differences is indicated from the fact 
that four of the species were originally classified and described under 



310 University of California Publications in Agricultural Sciences [Vol. 6 

three other genera, Hieracium, Cymboseris, and Phaecasium. Another 
was named for Pterotheca although the resemblance is only super- 
ficial. An interesting difference in chromosome morphology is the distal 
satellite on the C chromosome in pulchra, in its close relative, granatensis, 
and in pterothecoides, which resembles pulchra more than it does any 
other member of the series, although it is a distinct species. Since the 
preparation of this figure similar distal satellites have been discovered 
in palaestina and reuteriana, which are more closely related to pul- 
chra than are the remaining species. The possibility that the genom 
characterizing this group was derived from some 5-paired ancestor has 
been mentioned. The suggestion comes from the fact that equiarmed A 
chromosomes are unique in Crepis, being found in only two other series 
(cf. figs. 14 and 15). If the putative ancestor had J-shaped A's and a 
pair of E's, it is conceivable that reciprocal translocation between A 
and E, followed by meiotic irregularities, might result in the V-shaped 
A chromosomes and elimination of the rest of the E chromosome, thus 
establishing this 4-paired type. Translocations between nonhomologous 
chromosomes, such as might lead to the origin of new chromosome num- 
bers, have been observed in animals and plants, and Navashin (1932) 
has proposed a hypothesis of evolution of chromosome numbers based 
partly on the observation of such phenomena in Crepis. 

The oreades-suffreniana series is represented in figure 13. There is 
fairly close correspondence between the genoms of oread es and tectorum 
and the two species occur in the same region of northern Asia. Although 
robertioides and parviflora are less similar in their haploid genoms, they 
both occur in Asia Minor and are probably distantly related. Both 
oreades and robertioides are woody-based perennials and in other re- 
spects also are more primitive than the other species in this series. 
Furthermore, oreades is much more primitive than robertioides. The 
other species are annuals (nicaeensis is often biennial) and progres- 
sive reduction in size of plant and parts reaches a climax in the low, deli- 
cate, short-lived forms of the negleeta-suffreniana group. Corresponding 
reduction in size of the chromosomes is very notable in this series. Crepis 
capillaris must now share its distinction as a 3-paired species with fuligi- 
nosa. In the latter it seems to be the C chromosome which is lacking, 
while in capillaris it is the B, but the distinction between B and C chro- 
mosomes is an arbitrary one. It may be significant, however, that the A 
and D chromosomes are present in both of these plants. 

Crepis neglecta, sensu lato, presents a unique situation in respect to 
the chromosomes. In taxonomic treatments of this assemblage both cre- 
tica and fuliginosa have been classified in subspecific categories under 
neglecta. The morphological resemblances existing among the three en- 
tities are perhaps sufficient grounds for such a systematic treatment. In 
adopting it, however, it must be recognized that the divergence in chro- 



1934] Babcock-Cameron : Chromosomes and Phylogeny in Crepis. II 311 

mosome number, size, and shape is unusually great for a single species. 
With this frank admission there would seem to be no serious objection to 
such classification. For the cytological criterion is not of paramount 



»-<i 



suffreniana 



cretica neglecta fullginosa 



(OJ ID 

nicaeensla capillaris 



parviflora 



tectorura 



71C> in» 

oreadea robertloidea 

Fig. 13. Species of Eucrepis with n = 4 and 3. 

importance : in spite of the differences in number and morphology of the 
chromosomes, essentially the same residual complement of genes may be 
present in all three entities. Critical comparison, however, reveals a num- 



312 



University of California Publications in Agricultural Sciences [Vol. 6 



ber of significant morphological differences and these, together with the 
outstanding chromosomal differences, will justify recognition of the 
three as distinct, though very close, species. C. suffreniana, while closely 
related to neglecta, is beyond doubt a distinct species and its A and B 
chromosomes are notably different from those of neglecta, fuliginosa, 
and cretica. 



((Ku 



mungieri 



w< 



montana 



hierosolymltana 



willemetioidea 



Ot?m otai 



pygmaea 



lyrata 



moll i 3 
Fig. 14. Species of Eucrepis with n ■ 



Preliminary study of the haploid genoms of C. biennis and C. ciliata, 
in both of which In = ±40, indicates that they are certainly octoploids, 
based on» = 5, as has been previously reported for C. biennis (Collins 
and Mann, 1923). In both species there are two sizes of D chromosomes 
which may indicate hybrid origin. Further study is reported elsewhere 
(Babeock and Swezy, 1934) . 

Figure 14 shows the haploid genoms of the 6-paired Eucrepis spe- 
cies. The species are arranged in the same relative positions as shown in 
figure 4, these positions being determined on the basis of comparative 



1934] Babcock-Cameron: Chromosomes and Phytogeny in Crepis. II 313 

morphology, as summarized earlier, and geographic distribution. C. 
mollis extends from western Europe to middle Russia ; pygmaea occurs 
only in the European Alps, montana only in Greece, and mungieri only 
in Crete; while lyrata is found in western Siberia, willemetioides in 
northeastern Persia, and hierosolymitana in Palestine, Syria, and Cy- 
prus. The wide distribution of the series as a whole and of its most primi- 
tive member indicates relative antiquity, and necessitates the accept- 
ance of 12 as a primitive number in Eucrepis, unless it be assumed that 
these species originated through hybridization between 5-paired species, 
followed by amphidiploidy and consequent transformation and elimina- 
tion of certain chromosomes. This assumption is well supported by the 
following comparative classification of chromosome types in the haploid 
genoms of the seven species. 

mollis 2 A (1 V, 1 compound), B, C, 2 D lacking satellite. 

pygmaea 2 A (both V's, 1 with satellite), B, 2 C, E. 

lyrata 3 A (1 V, 2 with satellite), 2 C, E. 

montana 2 A (1 V), B with satellite, 2 C, E. 

mungieri A, B, C?, D, 2 E. 

willemetioides 2 A (1 V, 1 with satellite), B, C, 2 E. 

hierosolymitana 2 A (1 V, 1 compound), B, C, D lacking satellite, E. 

The foregoing classification is made by comparing each chromosome 
with the characteristic types in a basic 5-paired genom ; it does not de- 
pend on the order of arrangement within the haploid groups shown in 
figure 14. The presence of E chromosomes in all but one of the seven 
species, the duplication of E, D, C, and A chromosomes, and the striking 
alterations of A chromosomes in most of these species, all strongly indi- 
cate hybrid origin and that the parental species involved had five pairs 
of chromosomes. 

The genoms of the 7-paired Eucrepis species are shown in figure 15. 
The general similarity of the chromosome types is in agreement with 
the evidence from external morphology indicating that these are closely 
related species. But there are notable differences among the first three 
chromosomes from the right end of each haploid group. Like the 6-paired 
species this is a widely distributed and relatively ancient group, the 
members of which have become much reduced and considerably special- 
ized concomitantly with their adaptation to the rigors of alpine and 
arctic environments. This seems to indicate that 14 is also a primitive 
number in Crepis. But here also it is not difficult to imagine that these 
species originated through hybridization of 5-paired species plus am- 
phidiploidy, followed by transformation and elimination of some chro- 
mosomes. The presence of E chromosomes and more than one pair of 
certain chromosome types in all three species strongly supports this 
hypothesis. Two species are known from very high altitudes in the Hima- 
laya Mountains. These might have been the parents of this group, but 



314 University of California Publications in Agricultural Sciences [Vol. 6 

unfortunately they have not been studied cytologically. Even if they 
should not have the proper chromosome number and morphology, how- 
ever, this would not greatly discount the hypothesis here advanced. The 
possibility should also be noted that both putative parents were 4-paired 
species and that these 7-paired species are modified derivatives from a 
16-chromosome amphidiploid. At any rate it is hardly justifiable to con- 



inuu 



f lexuosa 



tniM'c 



elegans 



n-n,»)> 



nana 
a 



hi) ir 



gl gr oc 

b 
Fig. 15. a, Species of Eucrepis, with n = 7; b, representatives of the two 
pairs of D chromosomes of glauca (gl), gracilis (gr), and occidentalis (oc), 
indicating origin of all three groups of American species with n = 11 
through interspecific hybridization and amphidiploidy. 

elude that either 12 or 14 is a truly primitive number in Eucrepis until 
it is shown that the species under discussion could not have originated 
through interspecific hybridization and amphidiploidy. 

Analysis of the distribution of chromosome types in the octoploid and 
decaploid species has not been attempted. In some of the 22-chroniosome 
American species, however, there is definite cytological evidence indi- 
cating the manner of their origin. It is noteworthy that the number, 22, 
could not have arisen by autotetraploidy from any haploid number 
known in Crepis, although it is conceivable that autotetraploids with 



1934] Bab cock-Cameron: Chromosomes and Phylogeny in Crepis. II 315 

twenty or twenty-four chromosomes might have produced 22-chromo- 
some derivatives. But preliminary studies of the genoms of some 22- 
chromosome species indicate that they cannot be autotetraploids. This 
is most clearly demonstrated by comparison of the two pairs of satellite- 
bearing chromosomes found in each of these species. In figure 15& are 
shown representatives of the two pairs of D chromosomes from each of 
three species, glauca, gracilis, and Occident alls, representing the three 
subgroups of this assemblage. In occidentalis the difference is slight 
but in glauca and gracilis there are obvious differences in size of the 
two pairs. This evidence, together with 11 as the haploid number 
for ten species, is sufficient proof that all the American species except 
nana and elegans originated through hybridization of 8- and 14— chro- 
mosome species followed by amphidiploidy. 

Barkhausia 

The 10-chromosome Barkhausia species are compared with reference 
to their haploid genoms in figure 16. It will be recalled that albida is cer- 
tainly the most primitive member of this series and that alpina is its 
nearest relative. The proximal arm is longer in the A and C chromo- 
somes of albida; also the D and E chromosomes are larger in this species. 
C. syriaca is believed to have originated through hybridization of two 
alpina subspecies followed by genie mutation and chromosomal modifi- 
cation. Indigenous plants possess supernumerary chromosomes, mostly 
of one type, which is not shown here as part of the basic haploid genom 
for reasons advanced by Cameron (1934). The basic genom of syriaca 
resembles closely the haploid group of alpina. These two closely re- 
lated species are natives of Asia Minor and the Caucasus while rubra 
occurs in Crete, the southern Balkans, and Italy. C. rubra must be con- 
sidered a more recent species because of reduction in size of plant and 
especially because of its pink flowers as contrasted with the yellow 
flowers which occur in all other Barkhausia species. Furthermore, its 
scape-like flower stems point to some species other than alpina or albida, 
although this species doubtless arose from the same ancestral stock as 
the two latter. It is not surprising, therefore, to find some striking differ- 
ences in chromosome morphology in rubra, but the larger size of its 
chromosomes makes it another illustration showing that reduction in size 
of the chromosomes does not always accompany higher development. 
The commutata-thomsonii series has a markedly uniform type of ge- 
nom, as would be expected from the similar morphology of the four 
species. The genom of C. bureniana is included in figure 16 because, on 
morphological grounds, this species is certainly related to foetida or 
thomsonii and because, judging from geographical distribution, the lat- 
ter is probably its closest relative. Its chromosomes, however, resemble 
those of alpina more than those of thomsonii although the genoms of the 



316 University of California Publications in Agricultural Sciences [Vol. 6 

two latter species are undoubtedly similar. This suggests several pos- 
sible modes of origin for C. bureniana, but these are all too vague to jus- 
tify further discussion here. An investigation of this species is in prog- 
ress. 



oui 



bureniana 



rubra thorns on il 



IffU 



syriaca 



r)m 



J>)< 



eritreensis 



lhn 



alpina foetida 



llih 



n<» 



albida commutata 

Fig. 16. Species of Barkhausia with n = 5 and 4. 

In figure 17 are shown the genoms of two related Barkhausia series. 
The strong general resemblance of the genoms is the most striking thing 
in this illustration and from the external morphology of these species 
it seems certain that they all arose from the same ancestral stock. The 
lower four are the more western species, of which fontiana and canarien- 
sis are recognized as more primitive; and the chromosomes of fontiana 
are definitely larger than any of the others. Of the remaining nine spe- 



1934] Babcock-Cavieron : Chromosomes and Phylogeny in Crepis. II 317 



hackelll taraxacoides 

nfi n?i "mj 

taraxacifolla myriocephala veaicarla 



lyblca hyemalis 



triaaii clausonla 

canarlensia hieracloides 

Kll mi 

fontiana dlvaricata 

Fig. 17. Species of Barlchausia with n = 4 and 8. 



318 University of California Publications in Agricultural Sciences [Vol. 6 

cies, the lower four are more primitive and their chromosomes are some- 
what larger. C. vesicaria, myriocephala, marschallii, and taraxacifolia 
are very closely related and their chromosomes show the closest simi- 
larity. The marschallii genom is not illustrated. This species is most 
closely related to taraxacifolia and its chromosomes resemble those of 
that species closely, except the B, which is more like the B of vesicaria-. 
That C. taraxacoides is an autotetraploid is clearly indicated by the 
virtual identity of its corresponding pairs of A, B, C, and D chro- 
mosomes; and they resemble those of vesicaria so nearly as to suggest 
this as the parent species. Furthermore, autotetraploid forms of vesi- 
caria have been discovered (table 1) which resemble the typical diploid 
form rather closely except in size throughout. But taraxacoides differs 
from vesicaria in certain important characters, particularly in the in- 
volucre. Therefore, if taraxacoides did spring from vesicaria through 
autotetraploidy, it was not a recent event. In hackelii the A, B, and D 
chromosomes are sufficiently unlike to suggest origin through amphi- 
diploidy with taraxacifolia as one parent. But no other species is known 
which, by its morphology and native habitat, could have been the other 
parent. Therefore, it seems more probable that hackelii also originated 
through autotetraploidy and that there has been some chromosomal 
alteration. 

The remaining 4-paired Barkhausia species are represented in figure 
18. There can be no doubt that aculeata, juvenilis, and amplexifolia 
are closely related species and that the last is the most highly special- 
ized. Its chromosomes are much smaller than those of the other two. The 
C chromosome of juvenalis, however, is smaller than that of aculeata, 
yet juvenalis is less reduced in size of heads and achenes than aculeata, 
though in size of plant it is smaller. In comparing the chromosomes of 
aspera and setosa it may be noted that the "A" and "B" of aspera might 
well be interchanged; they would then compare fairly closely with 
the A and B of setosa. At any rate, the most striking differences in the 
two genoms are found in the C and D chromosomes. In size of heads 
and achenes setosa is more reduced than aspera, yet it has about the 
same total chromosome length. The genoms of the two perennial species 
are closely similar and they are probably about equal in age, although 
the fruits of bursifolia have become much more reduced and specialized, 
with a relatively long delicate beak, than those of bellidifolia. The same 
is true of senecioides and nigricans except that, in the former, reduction 
in size of fruits and specialization of the beak is even more extreme, and 
its chromosomes are definitely smaller. The notable difference in each 
of the four chromosomes is consistent with the morphological evidence 
that the two species are not closely related. In fact, from the achenes 
alone the closest relative of senecioides is bursifolia and the chromo- 
somes of the two species are similar except in size. 



1934] BabcocTc-Cameron : Chromosomes and Phylogeny in Crepis. II 319 



Clrj 



senecioides 



Tin 



nigricans 



setosa bursifolia 

aspera bellidlfolia 

Itfl rfr) o.$ 

aculeata juvenalis amplexifolia 

Fig. 18. Species of Barlchausia with n = 4. 



320 University of California Publications in Agricultural Sciences [Vol. 6 



SUMMARY AND CONCLUSIONS 

1. The genus. — Crepis is a natural group of more than two hundred 
species, distributed widely in the northern hemisphere and Africa. Some 
of them are common and well-known plants while many are extremely 
rare, little known, or occur only in relatively inaccessible places. In the 
past decade one hundred seven species of Crepis have been obtained in 
living condition from all parts of the world and examined cytologically. 
The present paper combines these cytological data with other evidence 
bearing on phylogenetic relationship. 

2. The subgenera. — Catonia with about one-fourth, Eucrepis with 
about one-half, and Barkhausia with the other fourth of the species, are 
the major natural subdivisions of the genus. They are characterized in 
the order just given by progressively greater specialization of the in- 
volucre and fruits, and along with this differentiation goes generally 
reduction in length of life-cycle and in size of the plant and its parts. 

3. Chromosome numbers in Crepis. — The series of characteristic 
diploid numbers found in the Old World species is 6, 8, 10, 12, 14, 16, 
40, and in North American species 22, 33, 44, 55 ( ?), 88 ( ?), besides 14 
in two representatives of an Old World group. Occasional irregidarities 
in these characteristic numbers occur and several species are known to 
have variable numbers. 

4. Chromosome numbers in the subgenera.— The mimber of species 
having a given chromosome number being indicated by an exponent, 
the distribution of chromosome numbers of Old World species is as 
follows : Catonia, 8 8 , 10 3 , 12 3 , 16 3 ; Eucrepis, 6 2 , 8 25 , 10 6 , 12 7 , 14 3 , (15-24) \ 
16\ 40 3 ; Barkhausia, 8 22 , 10 8 , ( 10-18) \ 16 2 . The American species are 
all of Eucrepis. 

5. The primitive numbers. — Although 8 is the most prevalent diploid 
number in the genus, 10 nmst be considered more primitive than 8 be- 
cause (1) the most primitive species in the genus, such as sibirica, 
pontana, and albida have 10; (2) no species with ten chromosomes are 
as greatly reduced or specialized as some of the species with eight chro- 
mosomes. If the 8-chromosome lines were derived from 10-chromosome 
ancestors, the most likely process would be by reciprocal translocations 
between nonhomologous chromosomes, followed by meiotic irregulari- 
ties leading to complete elimination of one pair of chromosomes. Such 
a process seems the most probable mode of origin of the 8-chromosome 
species, C. bureniana, and of the two 6-chromosome species, capillaris 
and fuliginosa. 

6. Ancient but doubtfully primitive numbers. — In addition to 10 and 
8, the numbers 12, 14, and 16 must be considered as possibly primitive in 
this genus. In Catonia there are three species with twelve chromosomes 



1934] Bdbcoclc-Cameron : Chromosomes and Phylogeny in Crepis. II 321 

which may be diploids, aneuploids, or polyploids; and there are three 
species with sixteen chromosomes, two of which are polyploids and one 
is still doubtful. In Eucrepis there are seven species with twelve, and 
three species with fourteen chromosomes. They are widely distributed 
and fairly primitive, yet it is possible that they are all polyploids of 
some sort. The one species with sixteen chromosomes is a tetraploid. In 
Barkhausia there are no species with twelve or fourteen and the two 
with sixteen chromosomes are tetraploids. In view of the small propor- 
tion of species having these numbers and the uncertainty that these 
species are simple diploids, the numbers 12, 14, and 16 cannot be ac- 
cepted as primitive. At least they are not basic like 8 and 10. 

7. Secondary numbers and modes of derivation. — Secondary numbers 
are 6, 12, 14, 15, 16, 22, other multiples of 11, and 40. Each of the two 
species with six chromosomes, capillaris and fuliginosa, was probably 
derived from a 4-paired ancestor. The most probable mode of origin of 
these 3-paired species has been described (cf. primitive numbers). It 
is conceivable that all the species with twelve and fourteen chromosomes 
were derived from amphidiploid hybrids. The constantly increasing 
evidence on the importance of amphidiploidy in the evolution of higher 
plants and the demonstration that it has played a definite role in 
Crepis lend support to this idea. All but one of the 16-chromosome 
species have been shown to be either autotetraploids or amphidiploids. 
The 22-chromosome species are the products of interspecific hybridiza- 
tion and amphidiploidy, and the higher-numbered American species 
are polyploids derived from them. One of the 40-chromosome species, 
biennis, is an octoploid (n = 5) and the closely related ciliata may be 
one also. The other 40-chromosome species, taygetica, is probably a 
decaploid (w = 4). Thus there are certainly two general processes by 
which new chromosome numbers have originated in Crepis, namely, by 
interspecific hybridization with amphidiploidy, and by polyploidy. It is 
also necessary to assume that some process, such as reciprocal transloca- 
tion, has led to reduction in number from 10 to 8 and from 8 to 6. The 
change from 10 to 8 is of basic importance in the evolution of the genus. 

8. Chromosome number and phylogeny. — Throughout the genus there 
is close correspondence between chromosome numbers and external 
morphology of the plants. The most primitive species have ten chro- 
mosomes but there are fairly primitive 8-chromosome types. In both 
10-chromosome and 8-chromosome series there is abundant evidence of 
progressive development from the woody-based perennial types with 
large simple leaves, few large heads, large florets, and large, unspecial- 
ized fruits to the short-lived annual forms with small or dissected leaves, 
numerous small heads, small florets, and very small or highly special- 
ized fruits. The basic, primitive number is 10 and there are three 5- 
paired phylogenetie lines, one in each subgenus. There is also sufficient 



322 University of California Publications in Agricultural Sciences [Vol. 6 

evidence that the subgenera are not separated by fixed limits. From 
the peculiarities of certain species, such as aurea and hypochaeridea in 
Catonia, patula, tingitana, and neglecta in Eucrepis, and albida and 
fontiana in Barkhausia, it is clear that Catonia tends to merge into 
Eucrepis and the latter into Barkhausia. From such evidence it appears 
highly probable that the three 5-paired phylogenetic lines, one in each 
subgenus, had their origin in a common nexus. At any rate the genus 
must be looked upon as a natural unit. 

9. Chromosome morphology in Crepis. — The chromosomes of Crepis 
species are of three distinct types, namely, those with a subterminal 
constriction, those with a subterminal constriction and bearing a satel- 
lite, and those with a median constriction. By comparing total length 
and relative length of the arms, chromosomes of the first general type 
are subdivided into classes known as A, B, and C. The satellite-bearing 
chromosome is called D and the small median-constricted chromosome, 
E. The only important exception to this general scheme is that in three 
subgroups under Eucrepis the large A chromosome has a median con- 
striction. 

10. The basic genom. — All the 5-paired species have one pair each of 
chromosome types A, B, C, D, E. 

11. Derived genoms and modes of derivation. — All the 4-paired species 
have types A, B, C, D. The two 3-paired species have A, B or C, and D. 
The 6-paired species are variable. In Catonia they seem to have two pairs 
of A chromosomes, one or two pairs respectively of B or C types, and 
one pair of D's. In Eucrepis they have one, two, or three pairs of A type 
(sometimes with median constriction, sometimes with a satellite or com- 
pound), one, two, or no pairs of D type, and no, one, or two pairs of B, 
C, and E types. This evidence on composition of the 6-paired genoms in- 
dicates that these species were derived from 5-paired ancestors through 
hybridization, and that 12 is not a primitive number in Crepis. The 
7-paired species have A, B, C, D, and E types with duplication of C, D, 
or E. This also suggests hybrid origin for these species and indicates 
that 14 is not a primitive number. All 8-paired species, so far as known, 
have only A, B, C, and D types and are polyploids. Analysis of distri- 
bution of chromosome types in the higher-numbered species has not been 
attempted, but dissimilarity of the satellite-bearing chromosomes in 11- 
paired American species adds sufficient proof of their origin through 
interspecific hybridization and amphidiploidy. Similar evidence is 
found in the two Old World octoploid species, C. biennis and C. ciliata. 

12. Chromosome morphology and phytogeny in Crepis. — (a) Morpho- 
logically similar species have similar chromosomes, (b) Similarity in 
chromosome types and in details of size and shape is an index of phylo- 
genetic relationship, (c) Both increase and decrease in chromosome size 
have occurred in the evolution of the genus, (d) There is a general ten- 



1934J Bab cock-Cameron : Chromosomes and Phytogeny in Crepis. II 323 

dency toward reduction of size of chromosomes concurrently with re- 
duction in size of the plant and reduction or specialization of organs. 
(e) There have been many changes in chromosome shape, as determined 
by relative length of the arms, and by these differences chromosomes of 
the same type from different species can be identified in hybrids. (/) 
This fact makes it possible, by analysis of the haploid genom, to deter- 
mine the mode of origin of certain species. 

13. Chromosomes and taxonomy. — Chromosome number and mor- 
phology is a taxonomic criterion of great value in this genus. But it must 
be used in connection with other available criteria such as comparative 
morphology and geographic distribution. Certainly, absolute identity of 
the chromosomes cannot be set up as of paramount importance in the 
classification of species, for specific entities are known in which the dif- 
ferent forms exhibit differences in number, size, or shape of the chro- 
mosomes. The genus is still evolving and visible changes in the chromo- 
somes are part of the process. 

14. Evolutionary processes in Crepis. — (a) In view of the evidence 
here summarized that there is one most primitive chromosome number 
and type of genom in Crepis, it is clear that the primary evolutionary 
process which has operated in the history of the genus, as we now know 
it, is some mode of transformation by which 8- and 6-chromosome spe- 
cies have been derived from 10-chromosome ancestors, (b) Next in im- 
portance is interspecific hybridization and amphidiploidy. (c) Third 
comes polyploidy, (d) Superimposed upon and operating concurrently 
with the foregoing is gene mutation, (e) Origin of species with new 
chromosome numbers through transformation and through interspecific 
hybridization with amphidiploidy must have occurred early in the evo- 
lution of the genus. (/) All four processes have been at work during 
comparatively recent times. 



324 University of California Publications in Agricultural Sciences [Vol. 6 



LITERATURE CITED 
Babcock, E. B. 

1931. Cytogenetics and the species-concept. Am. Nat., 45:1-18. 

Babcock, E. B., and Navashin, M. 

1930. The genus Crepis. Bibliog. Genet, 6:1-90. 

Babcock, E. B., and Swezt, 0. 

1934. The chromosomes of Crepis biennis L. and Crepis ciliata C. Koch. Cytologia 
(in press). 

Cameron, D. E. 

1934. The chromosomes and relationship of Crepis syriaca (Bornm.). Univ. Calif. 
Publ. Agr. Sci., 6:257-286. 

Collins, J. L., and Mann, M. M. 

1923. Interspecific hybrids in Crepis. II. A preliminary report on the results of 
hybridizing Crepis setosa with C. capillaris and biennis. Genetics, 8:212-322. 

HOLLINGSHEAD, L., AND BABCOCK, E. B. 

1930. Chromosomes and phyloger.y in Crepis. Univ. Calif. Publ. Agr. Sci., 6:1-53. 

Hooker, J. D. 

1882. Flora of British India, 3:399. 

Navashin, M. 

1925. Morphologische Kernstudien der Crepis-arten in Bezug auf die Artbildung. 

Zeitschr. f. Zellforseh. u. mikrosk. Anat., 2:98-111. 
1928. "Amphiplastie" — eine neue karyologische Erscheinung. Zeitschr. f.indukt. 

Abst. u. Vererb., Suppl. 2:1148-52. 

1932. The dislocation hypothesis of evolution of chromosome numbers. Zeitschr. f. 
indukt. Abst. u. Vererb., 63:224-31.